The invention relates to a method for determining waste products in the dialysis liquid in dialysis treatment.
Patients who have reduced kidney function or no kidney function at all get rid of waste products, including toxic substances, by dialysis treatment wherein the blood in an extracorporeal path via a membrane in the dialyzer is contacted with dialysis liquid containing different salts in such a concentration that the waste products by diffusion and convection pass through the membrane to the dialysis liquid and continue to a drain, the blood after having passed the dialyzer being returned to the patient.
The extent of the dialysis treatment that a patient shall be exposed to cannot be determined by feeling only; it is necessary to quantify in some way the result of the dialysis effect in order to avoid that the dialysis treatment will be insufficient. Considering that dialysis treatment is an expensive type of treatment, it is also just as important to avoid xe2x80x9covertreatmentxe2x80x9d of a patient. In other words, it is necessary to be able to control the efficiency of the dialysis treatment on-line, i.e. while the dialysis treatment is in progress, in order then to control manually or automatically the treatment by adjustment of the parameters of the dialysis machine in dependence thereof and thus to make the dialysis treatment more efficient.
In order to secure an adequate dialysis treatment the Kt/V(urea)-model has been developed (urea is one of the substances in the waste products used for measuring if an adequate treatment is offered), where K is the ability of the dialyzer to separate urea from the blood in ml/min, t is the treatment period in minutes, and V is the distribution of urea in the body in ml, which is related to the body weight of the patient. The non-dimensional factor Kt/V(urea) defines the reduction of the content of urea nitrogen in the blood and at three treatments each week should equal or be larger than 1 (at daily treatment the factor is lower than 1), and by using this factor it is possible to calculate the result of the treatment of the patient. The calculation of Kt/V(urea) is, however, complicated and requires that particularly the capacity of the dialyzer but also the accuracy of the dialysis machine and the distribution of the urea volume in the patient are accurately determined (Lindsay et al. Urea Monitoring During Dialysis: The wave of the future, Vol. XXXVIIxe2x80x94Trans Am Soc Arif Intern Organs 1991). The Kt/V(urea) -model is used but is not considered absolutely reliable due to inherent sources of errors which are related to measurement values and product precision.
It has been recommended to combine the Kt/V(urea)model with continuous determined of the percentage reduction of urea in the patient during the dialysis treatment, and a proposal along this line is Dianalyzer from Paradigm Biotechnologies, Toronto, Canada. The device comprises a computer to which such quantities, i.a. Kt/V(urea), are supplied, which as required for calculation of the percentage reduction of urea (PRU) in the patient. A plasma sample is taken via a plasma filter from the extracorporeal blood path and is mixed with enzyme solution and reagent, the mixture obtained then being examined optically in order to determine the amount of urea in the blood, which in turn is used for determining the time at which the dialysis treatment in progress should be stopped. In Dianalyzer sampling is effected a certain number of times during the dialysis treatment and, thus, no continuous measurement of the urea reduction is concerned. In order to measure the urea reduction in the blood it is necessary to have parameters available which either must be established by blood analysis or have to be estimated, which makes this type of measurement unsuitable for application on-line. The development of this measuring method has been focused substantially on the development of suitable sampling devices in combination with traditional analysis instruments.
An apparatus which functions in a similar way with chemical reagents for determining of Kt/v is Biostat(trademark)Urea Monitor from Baxter.
Monitoring of the urea content in the outlet flow of dialysis liquid provides greater flexibility as far as the applied measuring system is concerned, but so far the development has led up to manual sampling and the use of traditional measuring system. Samples of the dialysate therefor usually must be sent to a laboratory with the necessary measurement equipment.
Thus, it has been proposed (IEEE Engineering in Medicine and Biology Society 11th International Conference) for continuous monitoring of hemodialysis to measure enzymatically induced conductivity changes caused by hydrolyse of urea (or other important molecules) in the dialysis liquid, especially developed sensors being used for such measurement. A drawback of these sensors is that they are cumbersome to calibrate and that it can be difficult to compensate for existing background conductivity.
The invention relates to method and dialysis machine for determining the content of waste products in the outgoing dialysis liquid wherein the measurement of the concentration of a certain substance or a combination of substances included in the waste products is effected directly on the outgoing dialysis liquid from the dialyzer at dialysis treatment. Method and machine of this kind are disclosed in US-A-4,244,787 and WO-A-9408641.
The purpose of the invention is to provide a method for accurate determination of the amount of waste products in the dialysis liquid during dialysis treatment, which allows application of a technique known per se and the use of a reliable apparatus set and which allows that urea or some other substance included in the waste products is measures so that one can choose to make the determination by measuring the substances which are best suited for the election of dialyzer and the control of the dialysis machine in order to adapt the dialysis treatment to the patient.
For said purpose the method according to claim 1 and the dialysis machine according to claim 13 are proposed according to the invention.